Thread-cutting device for sewing machines

ABSTRACT

A thread-cutting device for sewing machines of the kind having a machine base plate with a side opening therein which accommodates the cloth plate of the machine and a removable slide plate allowing access to the space underneath the machine base plate, which thread cutting device is adapted to be mounted against the lower side of the slide plate. The thread-cutting device has a compact structure of a design allowing the device to be mounted on the slide plates of different types of sewing machines.

I United States Patent 1 1 31 4mm Van azendonk 1 an". M, W72

[54] THREAD-CUTTING DEVICE FOR [56] References Cited SEWING MACHINES UNITED STATES PATENTS [72] memo" iz 'z g'fi f f fi s g 3,524,420 8/1970 Peschke ..112/252 3,489,115 1/1970 Marforio ..1 12/252 [73] Assignee: DeJong & DeVlieger Machinehandel N.V.,

Zwanenburg/Halfweg, Netherlands Primary Examiner-James R. Boler [22] Filed Apr 27 1970 Attorney-Waters, Roditi, Schwartz and Nissen [21] Appl. No.: 32,032 [57] ABSTRACT A thread-cutting device for sewing machines of the kind hav- [30] Foreign Application Priority Data ing a machine base plate with a side opening therein which ac- Nov 13 1969 Netherlands 6917054 commodates the cloth plate of the machine and a removable slide plate allowing access to the space underneath the 52 us. 121 112/252 machine base Plate which Ming is mined [51] IHLCL 65/00 be mounted against the lower side of the slide plate. The [58] Field of Search ..112/252 thread-flitting device has a Compact Structure Of a desig" lowing the device to be mounted on the slide plates of different types of sewing machines.

7 Claims, 3 Drawing liigures warm 5% arch 2 Sheets-Sheet l Painted March 14, 1972 3,648,634

2 Sheets-Sheet 2 THREAD-CUTTING DEVICE FOR SEWING MACHINES BACKGROUND OF THE INVENTION The invention relates to a thread-cutting device for sewing machines and more in particular to such a device for sewing machines of the conventional kind having a machine base plate with a side opening therein which accommodates a cloth plate and a removable slide plate adjacent the cloth plate allowing access to the space underneath the cloth plate and base plate in which the stitch forming means, such as the bobbin and rotary hook mechanism, are arranged.

When providing sewing machines of this type with a threadcutting device for cutting the sewing threads, it has been the usual practice to mount the thread-cutting device to one side of the slide plate against the lower side of the machine base plate. Generally, however, at this location there is only little room available which makes it necessary to adapt the dimensions, shape and design of the thread-cutting device to the sewing machine concerned. It is thus not possible to use the same thread-cutting device for all types and different makes of sewing machines which are sold on the market. In most cases sewing machines for industrial use are delivered by the manufacturer without thread-cutting device and the user of the machine, should he want such an accessory, must himself arrange for the instalment thereof. The manufacturer or supplier of the thread-cutting device who has to perform this task is thus forced to keep in stock a great number of thread-cutting devices of different design and configuration adapted to the several types of sewing machines on the market while also the manner of mounting the thread-cutting device is different for each sewing machine type. Thereby the manufacturing and mounting costs of the thread-cutting device are considerably increased.

SUMMARY OF THE INVENTION The invention has for its main object to obviate these disadvantages and to make it possible to use identical threadcutting devices for different types of sewing machines of the above-described kind which devices can be mounted in A machines in a uniform manner.

Another object of the invention is to provide such a threadcutting device which has a simple and compact design and can be easily and quickly mounted in the sewing machine concerned in the correct position with respect to the stitch forming means thereof.

According to the invention, the thread-cutting device is mounted against the lower side of the slide plate of the sewing machine adjacent the stitch forming means in a position for cutting the threads closely below the cloth plate.

Since all sewing machines of the kind described are provided with such a slide plate in the side opening of the machine base plate and since there is always space available beneath this side plate, it is thus possible to use a threadcutting device of uniform design for practically all types of the sewing machines concerned. Furthermore, there is the additional advantage that the mounting of the thread-cutting device onto the slide plate can be carried out when the latter is removed from the machine base plate which is, of course, much easier than securing the device against the lower side of the base plate itself in a position which is often difiicultly accessible.

The thread-cutting device may be of the type having a pneumatically driven cylinder and piston arrangement in which the piston is coupled to a flat hook-shaped cutting knife arranged for movement in a plane parallel to and closely below the cloth plate, which cutting knife on its actuation catches the sewing threads and pulls the latter towards a stationary cutting knife for the cutting of the threads. In known cutting devices of this type the cylinder is mounted against the lower face of the machine base plate to one side of the slide plate in which the outwardly projecting piston rod of the piston through a coupling mechanism drives the movable cutting knife with a swinging movement.

In order to obtain a compact configuration of the threadcutting device allowing the latter to be fitted underneath the slide plate, the cutting device of the invention, according to a preferred embodiment, comprises a cylinder block having a bore and adapted to be mounted against the lower side of the slide plate with the axis of the bore extending substantially normal to the front edge of the slide plate adjacent the cloth plate. A piston is arranged in the bore adapted to be pneumatically driven for reciprocating movement in this bore and is secured to a piston rod extending rearwardly from the piston in a direction away from said slide plate forward edge. The cylinder block has a recessed guide way formed in its upper face and extending parallel to the cylinder bore axis and a movable cutting knife having a hook-shaped forward end and a flat straight body portion is arranged for reciprocating sliding movement in this guide way in a position in which the knife forward end is directed towards the cloth plate. The body portion has its rear end secured to the rearwardly extending end of the piston rod to be driven thereby. A cover plate is secured against the upper face of the cylinder block for confining the movable cutting knife body portion in the recessed guide way which cover plate has an extension at its forward edge adjacent the cloth plate formed into a stationary cutting knife disposed above the movable cutting knife for cooperation therewith. In this way the movable cutting knife is disposed for linear reciprocating movement immediately above the cylinder and the piston rod to which it is coupled whereby the cutting device forms a compact structure of relatively small axial length and may be easily disposed in the space available below the slide plate.

Preferably, the guide way in the cylinder block has adjacent the forward edge of the slide plate a recess for accomodating a leaf spring which presses the movable cutting knife against the stationary knife in order to ensure a proper cutting action.

In the conventional sewing machines of the present kind the slide plate carries at its lower side a laterally projecting leaf spring which engages the edge portions of the base plate side opening in order to hold the slide plate in its closed position with a light clamping action. If, however, the slide plate carries the thread-cutting device as the invention suggests, this clamping action is generally insufficient to hold the slide plate in position against the forces acting thereon during the operation of the cutting device. For this reason, according to the invention the slide plate may be provided at both its sides with laterally projecting clamping members adapted to engage the underside of the machine base plate and carrying clamping screws for firmly securing the slide plate in the base plate.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate by way of example an embodiment of a sewing machine with a thread-cutting device according to the invention in which, however, only those parts of the sewing machine are shown as are necessary for a proper understanding of the invention.

FIG. l is a perspective view of a part of the sewing machine with the slide plate carrying the thread-cutting device removed from the side opening of the machine base plate;

FIG. 2 is an exploded view of the several parts of the threadcutting device; and

FIG. 3 is a perspective view from below of the machine part of FIG. 1, likewise with the slide plate shown in the position outside of the base plate side opening.

PREFERRED EMBODIMENT OF TI-IE INVENTION Referring to FIGS. 1 and 3 of the drawings, there is shown a sewing machine of conventional design having a machine base plate 1, a needle 2, a presser foot 3 and a cloth plate 4 with cloth advancing feed dogs 5 which are driven by a feed dog driving arm 6 in a known manner. The machine base plate 1 has at its left hand side a side opening; 7 formed therein, the cloth plate 4 being secured at the inner end of this side opening. The side edges of this opening 7 are grooved to form lateral guides for accommodating a slide plate 8 which in its closed position lies with its forward edge 9 against the rear edge of the cloth plate 4. The slide plate covers the underlying space which accommodates a rotary loop-taking hook member 10 revolving about the bobbin for the lower thread (not shown) and cooperating with the needle carrying the upper thread for the formation of sewing stitches in a known manner. The above-mentioned parts of the sewing machine are of conventional design and need, therefore, not be described in further detail.

A pneumatically actuated thread-cutting device, generally indicated by 11, is mounted against the lower side of the slide plate 8. Referring also to FIG. 2, this thread-cutting device comprises a rectangular cylinder block 12 having a bore 13 in which a piston 14 secured to a piston rod 15 is arranged for reciprocating movement. A U-shaped guide block 16 is fitted against the rear side of the cylinder block 12 and is secured to the latter by means of socket-head screws 17 passing through the legs of the guide block. The central body portion of the U- shaped guide block forms an airtight closure for the open rear end of the cylinder bore 13 and is itself provided with a bore 18 for the passage of the piston rod 15, an O-ring 19 forming a seal between the piston rod and the wall of this bore. The piston rod 15 thus extends rearwardly through the body portion and between the two legs of the U-shaped guide block 16.

A recessed guide way 20 is formed in the upper surface of the rectangular cylinder block 12 and extends above and in the direction of the axis of the cylinder bore 13 and the piston rod 15. TA corresponding recessed guide way 21 is formed in the body portion of the guide block 16 and forms an extension of the guide way 20. The upper edges at the inner sides of the legs of the U-shaped guide block 16 are recessed to form guide grooves 22 substantially in alignment with the guide way 20, 21. A coupling member or slide block 23 of T-shape is secured onto the rear end of the piston rod 15, the body portion of this coupling member fitting between the legs of the guide block 16 and the laterally extending upper flange parts of the coupling member slidably engaging in the recessed guide grooves 22. The upper surface of the coupling member 23 is coplanar with the bottom of the guide way 20, 21.

A flat elongated cutting knife 24 is disposed for reciprocating longitudinal sliding movement in the recessed guide way 20, 21. The movable cutting knife 24 has at its forward end an integral hook portion 25 with a pointed end, and adjacent its rear end two holes 26 for receiving the upper ends of two pins 27 mounted in corresponding holes in the upper portion of the coupling member 23. The elongated movable cutting knife 24 thus extends axially above the piston rod 15 and the cylinder bore 13 and on the actuation of the piston 14 this knife can be moved between a rear rest position in which the hook portion 25 still projects past the forward edge 9 of the slide plate 8 (FIG. 3) and a forward position (FIG. 1) in which the hook portion 25 may catch the sewing threads just below the cloth plate 4. The cylinder block 12 and the guide block 16 are provided with conduits (not shown) which communicate with the cylinder bore on both sides of the piston 14 and in which threaded nipples 28 have been screwed for the connection of flexible tubes 29 leading to a suitable pneumatic control system (not shown).

A cover plate 30 is arranged against the upper side of the cylinder block 12 and the guide block 16 which cover plate thus confines the movable cutting knife 24 in its guide channel 20, 21. The cover plate 30 has an integral forward extension of smaller width forming a stationary knife 31 projecting past the forward edge 9 of the slide plate 8 and disposed above the projecting hook portion 25 of the movable knife 24. At its forward end the stationary knife 31 is formed into a downwardly inclined cutting edge 32. A recess 33 has been formed in the bottom of the guide way 20 adjacent the forward end of the cylinder block 12 and a curved leaf spring 34 is disposed in this recess so as to press the movable cutting knife 24 against the cutting edge 32 of the stationary knife 31.

The slide plate 8 has four holes 35 arranged in alignment with elongated holes 36 in the cover plate 30 and with threaded holes 37 in the cylinder block 12 and the guide block 16, respectively. Screws 38 of the socket-head type passing through the holes 35 and 36 are screwed into the threaded holes 37 which screws on being tightened thus firmly secure the cylinder block and the guide block to the slide plate 8. The

, elongated holes 36 in the cover plate 30 allow the position of the latter to be adjusted lengthwise for the proper adjustment of the position of the cutting edge 32 of the stationary knife 31 with respect to the hook portion 25 of the movable knife 24.

As appears from the drawings, the dimensions of the combined cylinder block and guide block are such that the device easily fits underneath the slide plate 8, the height of this combined block being small enough to leave sufficient room for the bobbon of the lower thread of the sewing machine to be mounted in the usual manner on the rotary hook member 10.

At each lateral side of the slide plate 8 a clamping member 39 has been secured by means of a screw bolt 40 against the lower side of the slide plate which clamping members project laterally past the side edges of the slide plate 8 and are adapted to engage underneath the side edge portions of the opening 7 in the base plate 1 whereby the slide plate can be firmly but removably secured in this opening by tightening the bolts 40.

When the above-described thread-cutting is to be mounted in a sewing machine, the slide plate 8 of machine is removed from the base plate 1 and the four holes 35 for the passage of the screws 38 and two screw holes 41 for receiving the clamping bolts 40 are bored in this slide plate. The device is then secured against the lower side of the slide plate by means of the socket-head screws 38. Lastly, the slide plate 8 is placed into the opening 7 and secured to the base plate 1 by means of the clamping members 39 and bolts 40. The mounting of the thread-cutting device is thus very simple and because of its small dimensions and its position directly below the slide plate 8 the device is suitable for use in substantially all types of sewing machines of the present kind.

The flexible tubes 29 may be connected to any suitable pneumatic control system for actuating the thread-cutting device. For instance, the tubes 29 can be connected to electromagnetically actuated valves which are controlled in the manner as described in applicants copending patent application Ser. No. 784,770, filed Dec. 18, 1968, now patent No. 3,578,770. When the sewing threads must be cut, that threadcutting device is actuated when the needle 2 has reached its highest position whereby the piston 14 in the cylinder bore 13 is driven pneumatically from its left hand rest position to the right (as seen in FIGS. 1 and 3). The hook portion 25 of the movable cutting knife 24 thus moves forwardly close beneath the cloth plate 4 and seizes the sewing threads in its hook. Immediately thereafter the piston is returned to its rest position whereby the hook portion 25 carries the sewing threads along towards the cutting edge 32 of the stationary knife 31 to cut the threads at this cutting edge.

Although the invention has been shown and described with reference to a preferred embodiment thereof, other embodiments may be resorted to within the scope of the following claims.

What is claimed is:

1. The combination of a sewing machine with a threadcutting device, said sewing machine including a machine base plate having a side opening therein, a cloth plate mounted in said base plate side opening, stitch forming means arranged in the space extending underneath said base plate, cloth plate and side opening, and a removable slide plate slidably mounted in said base plate side opening with its front edge adjacent said cloth plate and allowing access to said space, said thread-cutting device comprising a cylinder block provided with a bore and having a smaller width than said slide plate, said block being mounted against the lower side of the slide plate within the lateral extension of said slide plate and with the axis of said bore extending substantially normal to the slide plate front edge, a piston member arranged in said bore for reciprocating movement therein, a piston rod secured to said piston member and extending from the latter rearwardly in a direction away from said slide plate forward edge, pneumatic means connected with said cylinder block for driving said piston in said bore with a reciprocating movement, said cylinder block having a recessed guide way formed in its upper face and extending parallel to said bore axis, a movable cutting knife having a hook-shaped forward end and a flat straight body portion arranged for reciprocating sliding movement in said guide way in a position in which said forward end is directed towards said cloth plate, a coupling member secured to the rear end of said cutting knife body portion and to the rearwardly extending end of said piston rod, a cover plate secured against the upper side of said cylinder block for confining said movable cutting knife body portion in said recessed guide way, said cover plate having at its forward edge adjacent said cloth plate an extension formed into a stationary cutting knife disposed above said movable cutting knife for cooperation therewith in cutting the sewing threads closely below the cloth plate and means for securing said cylinder block and cover plate against the lower side of said slide plate with said cover plate clamped between said block and slide plate.

2. The combination of claim 1, further comprising a guide block arranged against the cylinder block and forming a guide for said coupling member and for said body portion of said movable cutting knife, said guide block being likewise covered by said cover plate.

3. The combination of claim 1 in which a recess is formed in said guide way of said cylinder block adjacent the forward end thereof, a leaf spring being disposed in said recess for pressing said movable cutting knife against said stationary cutting knife.

4. The combination of claim 1 further comprising clamping means mounted against the lower side of the slide plate adjacent the side edges thereof and extending laterally past said side edges for engaging said base plate and clamping bolts cooperating with said clamping means for firmly but removably securing said slide plate in said base plate side opening.

5. A thread-cutting device for a sewing machine of the type having a base plate with a side opening and a slide plate arranged in this side opening, said thread'cutting device com prising a cylinder block having a smaller width than said sewing machine slide plate and adapted to be mounted against the lower side of said slide plate, said cylinder block having a bore and a forward and a rear end, a piston member arranged in said bore for reciprocating movement therein, a piston rod secured to said piston member and extending from the latter rearwardly past said cylinder block rear end, said cylinder block having means adapted to connect the same to pneumatic actuating means for driving said piston in said bore with a reciprocating movement, said cylinder block further having a recessed guide way formed in its upper surface and extending parallel to the axis of said bore between said forward and rear end of said block, a movable cutting knife having a hookshaped forward end and a flat straight body portion arranged for reciprocating sliding movement in said guide way in a position in which said knife forward end projects past said cylinder block forward end, a coupling member secured to the rear end of said cutting knife body portion and to the rearwardly extending end of said piston rod, a cover plate fitting against the upper side of said cylinder block for confining said movable cutting knife body portion in said recessed guide way, said cover plate having an extension projecting forwardly past said cylinder block forward end and forming a stationary cutting knife disposed above said movable cutting knife for cooperation therewith, and means for securing said cylinder block and cover plate against the lower side of said slide plate with said cover plate clamped between said block and slide plate.

6. The tread-cutting device of claim 5 further comprising a guide block secured against said cylinder block rear end forming a guide for said coupling member and for said body portion of the movable cutting knife, said guide block being likewise covered by said cover plate.

7. The thread-cutting device of claim 5 in which a recess is formed in said guide way of said cylinder block adjacent the forward end thereof, a leaf spring being disposed in said recess for pressing said movable cutting knife against said stationary cutting knife. 

1. The combination of a sewing machine with a thread-cutting device, said sewing machine including a machine base plate having a side opening therein, a cloth plate mounted in said base plate side opening, stitch forming means arranged in the space extending underneath said base plate, cloth plate and side opening, and a removable slide plate slidably mounted in said base plate side opening with its front edge adjacent said cloth plate and allowing access to said space, said thread-cutting device comprising a cylinder block provided with a bore and having a smaller width than said slide plate, said block being mounted against the lower side of the slide plate within the lateral extension of said slide plate and with the axis of said bore extending substantially normal to the slide plate front edge, a piston member arranged in said bore for reciprocating movement therein, a piston rod secured to said piston member and extending from the latter rearwardly in a direction away from said slide plate forward edge, pneumatic means connected with said cylinder block for driving said piston in said bore with a reciprocating movement, said cylinder block having a recessed guide way formed in its upper face and extending parallel to said bore axis, a movable cutting knife having a hook-shaped forward end and a flat straight body portion arranged for reciprocating sliding movement in said guide way in a position in which said forward end is directed towards said cloth plate, a coupling member secured to the rear end of said cutting knife body portion and to the rearwardly extending end of said piston rod, a cover plate secured against the upper side of said cylinder block for confining said movable cutting knife body portion in said recessed guide way, said cover plate having at its forward edge adjacent said cloth plate an extension formed into a stationary cutting knife disposed above said movable cutting knife for cooperation therewith in cutting the sewing threads closely below the cloth plate and means for securing said cylinder block and cover plate against the lower side of said slide plate with said cover plate clamped between said block and slide plate.
 2. The combination of claim 1, further comprising a guide block arranged against the cylinder block and forming a guide for said coupling member and for said body portion of said movable cutting knife, said guide block being likewise covered by said cover plate.
 3. The combination of claim 1 in which a recess is formed in said guide way of said cylinder block adjacent the forward end thereof, a leaf spring being disposed in said recess for pressing said movable cutting knife against said stationary cutting knife.
 4. The combination of claim 1 further comprising clamping means mounted against the lower side of the slide plate adjacent the side edges thereof and extending laterally past said side edges for engaging said base plate and clamping bolts cooperating with said clamping means for firmly but removably securing said slide plate in said base plate side opening.
 5. A thread-cutting device for a sewing machine of the type having a base plate with a side opening and a slide plate arranged in this side opening, said thread-cutting device comprising a cylinder block having a smaller width than said sewing machine slide plate and adapted to be mounted against the lower side of said slide plate, said cylinder block having a bore and a forward and a rear end, a piston member arranged in said bore for reciprocating movement therein, a piston rod secured to said piston member and extending from the latter rearwardly past said cylinder block rear end, said cylinder block having means adapted to connect the same to pneumatic actuating means for driving said piston in said bore with a reciprocating movement, said cylinder block further having a recessed guide way formed in its upper surface and extending parallel to the axis of said bore between said forward and rear end of said block, a movable cutting knife having a hook-shaped forward end and a flat straight body portion arranged for reciprocating sliding movement in said guide way in a position in which said knife forward end projects past said cylinder block forward end, a coupling member secured to the rear end of said cutting knife body portion and to the rearwardly extending end of said piston rod, a cover plate fitting against the upper side of said cylinder block for confining said movable cutting knife body portion in said recessed guide way, said cover plate having an extension projecting forwardly past said cylinder block forward end and forming a stationary cutting knife disposed above said movable cutting knife for co-operation therewith, and means for securing said cylinder block and cover plate against the lower side of said slide plate with said cover plate clamped between said block and slide plate.
 6. The thread-cutting device of claim 5 further comprising a guide block secured against said cylinder block rear end forming a guide for said coupling member and for said body portion of the movable cutting knife, said guide block being likewise covered by said cover plate.
 7. The thread-cutting device of claim 5 in which a recess is formed in said guide way of said cylinder block adjacent the forward end thereof, a leaf spring being disposed in said recess for pressing said movable cutting knife against said stationary cutting knife. 